SSS11.1

Land degradation represents one the main issue affecting agricultural systems, especially in those areas that are characterized by agricultural practices on steep hillslopes. The occurrence of erosion processes and landslides is closely linked with the presence of road networks. Factors like inefficient of absent drainage systems, wasteful road management and not optimal planning, as well as specific geomorphological and hydrological elements directly encourage landslides activation. In this connection, the combined use of Remotely Piloted Aircraft Systems (RPAS) and photogrammetric techniques (e.g. Structure from Motion; SfM) allowed to elaborate multi-temporal (therefore 4D) high-resolution Digital Elevation Models (DEMs), so as to detect geomorphological changes affecting earth surface at specific spatial and temporal scale. At the same time, the adoption of several models allows to compute specific hydrological analysis, for instance investigating the alteration of surface water flow dynamics due to the presence of specific features like roads. In this context, this research aims to propose a multi-temporal analysis of the road-induced water flow alterations in a shallow landslide-prone agricultural system. SIMWE model (Mitasova et al., 2013) was applied focusing on different geomorphic and rainfall scenarios, looking at the presence of the road network within the study area and assuming its absence through specific DEM post-processing procedures. In this connection, the possibility to perform multi-temporal hydrological simulations at the hillslope scale, to analyse the role played by the road in landslides activation is still a challenge to be investigated. In this article, we considered a case study placed in northern Italy, where two shallow landslides were observed below a rural road located within a terraced vineyard. Multi-temporal hydrological simulations were conducted to further analyse the evolution of road induced water flows deviations, thus stimulating landslides occurrence on the detected hillslopes. Maximum water depths equal to 0.60 m and 0.46 m were noticed close to specific zones of the road sections located above the first and the second landslide respectively. The simulations computed assuming the absence of the road revealed the lack of water flows deviations involving the landslide zones, underlining the fact that the road absence would avoid significant changes in water flow paths toward the collapsed zones. The key role played by the road in water flows deviation and in the evolution of the observed land degradation dynamics was attested through the comparison of the thematic maps resulted from each simulation. This work could be a solid starting point for further analyse the roads impact on runoff dynamics at a wider scale, aiming to plan and propose mitigation interventions so as to reduce the occurrence of future risk scenarios. At the same time, efficient design of drainage systems along the roadway could be conducted starting from the outcomes presented in our research, so as to prevent the activation of similar land degradation processes.

Reference
Mitasova H., Barton C.M., Ullah I., Hofierka J., Harmon R.S. 2013. GIS-Based Soil Erosion Modeling. Treatise on Geomorphology (3), 228-258.

How to cite: Mauri, L., Straffelini, E., and Tarolli, P.: Modelling of overland flows in a terraced vineyard affected by road-induced shallow landslides, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4955, https://doi.org/10.5194/egusphere-egu21-4955, 2021.

The present study is to quantify the spatial-temporal pattern of the Land Use/ Land Cover Change (LULCC) during a decade (i.e., 2010 to 2020) in the Dehradun city which is situated in the foothills of the Himalaya, using Landsat data. The study helps in identifying the major bio-physical factors governing LULCC through modern geospatial techniques. Change detection shows that the study area experienced an increase in its urban area from 2010 to 2020 and a comparatively decrease in cropland and forest area. This was due to an increase in its urban population, rapid increase in industrialization and tourism during the same period. The change detection analysis further shows that 2010-2020, associated with change in croplands, change in built-up, forest lands, change in water-bodies, water levels, and rainfall. With comparison of above results and collected socio-economic data in this region, the impact of changing land use & bio-physical/ economic factors on agricultural profitability were analyzed. The result of this study could thus lead to a detailed and lucid spatiotemporal assessment of the major bio-physical factors. It is expected that the study will help in facilitating better policy making and infrastructure development for industries and urbanization.

How to cite: Singh, G.: A study of decadal Land use-land cover change in Dehradun city., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14196, https://doi.org/10.5194/egusphere-egu21-14196, 2021.

Erosion effect plays a significant role in the run-out process of a rapid loess landslide. This effect is manifested in bed entrainment and frontal plowing on terraced material during movement, leading to the volume amplification. Therefore, an improved two-layer model is proposed to describe the frontal plowing and bed entrainment in this paper. In addition, the bed entrainment rate is further calculated by introducing the bed entrainment physical model. The sliding mass and plowed material are assumed to be immiscible in this model, and the mechanical behaviour between the materials is simulated by considering the interaction force between the two layers. Furthermore, the governing equations are deduced from the mass and momentum conservation. It is then applied to analyze a typical rapid loess landslide, Dongfeng landslide. The results indicate that the bed entrainment and frontal plowing have a significant impact on the mobility of the landslide, which is mainly shown in the following two aspects: 1) the bed entrainment effect significantly increases the speed and volume of the landslide; 2) The frontal plowing effect will impede the motion of the frontal sliding mass, and there is a clear separation between the sliding mass and the plowed material, which is more consistent with the field observations. The improved two-layer model proposed in this paper can provide more reliable assessment to describe the rapid loess landslides with erosion.

How to cite: Shen, Y., Li, T., Li, D., and Nian, T.: Erosion effect in the movement process of rapid loess landslide using an improved two-layer model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7841, https://doi.org/10.5194/egusphere-egu21-7841, 2021.

A large number of radionuclides, produced by nuclear accidents or nuclear waste, may cause radioactive contamination in the agricultural and aquatic ecosystems. Under these circumstances, it is necessary to optimize the remediation of agricultural areas polluted by radionuclides using innovative monitoring and prediction techniques. To mitigate radioactive contamination in farmland soil and effectively protect groundwater, some measures should be taken against on field investigation, laboratory experiment and model prediction. In this study, the HYDRUS-1D model was used to simulate the vertical migration of ¹³⁷Cs and ⁶⁰Co in farmland soil in northern China calibrating by the soil lysimeter experiment, and the scenario simulations of ¹³⁷Cs and ⁶⁰Co migration were conducted under different radioactive levels. Results showed that the order of sensitivity in saturated water content (θ_s), residual water content(θ_r), saturated hydraulic conductivity(K_s) and distribution coefficient (K_d) applied in HYDRUS 1D model was K_d > θ_s > θ_r >K_s. The simulated concentrations ​​of ¹³⁷Cs and ⁶⁰Co in Brown soil and Aeolian sandy soil on day 175 and 355 were significantly positively correlated with the measured values​​ (r>0.90, p<0.01). The verification results showed that the predictive values on the 577^th day were also significant positive correlated with the measured values ​​(r>0.90, p<0.01). The RMSE, CRM and NRMSE calculating by simulated and measured values ​​of ¹³⁷Cs and ⁶⁰Co in soil were very small, indicating that HYDRUS 1D can be used to simulate the migration of radionuclides in farmland soil. Scenarios simulation results revealed that radionuclides were concentrated in the surface layer within 5 cm, but the migration depth has exceed 10 cm soil depth, and even reaches up to 23.5 cm depth at high concentration level. The surface soil should be cleaned timely to protect groundwater with high level from radioactive contamination and further study should be done about horizontal transport and numerical simulation.

How to cite: Wenxiang, L., Hanqing, Y., and Yang, L.: Risk evaluation of radionuclides contamination on soil and groundwater under different scenarios simulating by HYDRUS-1D, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1209, https://doi.org/10.5194/egusphere-egu21-1209, 2021.

Abstract: Land use is one of the most important forms in agricultural production. Non-appropriate land use can cause deterioration of physical, chemical and biological properties of soil, thus affecting sustainable agriculture. Earlier reports showed that land use drastically altered microbial community composition. However, the mechanism of land use on microbial communities is still not fully understood. In the present study, we focus on the dry hot valley, characterized by high temperature and low humility, to test whether soil properties from four primary land uses including the land conversion from farmland (SLC), sugarcane land (SL), maize land with conventional tillage (CT) and bare land (BL) have different influences on soil microbial communities. The results showed that land uses altered bacterial and fungal community composition. In SL and BL, we found the respective absence of a kind of fungi at phylum the level. The abundances of several bacterial phyla in SL such as Gemmatimonadets and Acidobacteria associated with promoting mineralization were higher than that in other land uses. RDA indicated that bacterial communities were influenced by soil total nitrogen, total organic carbon and available potassium contents, and fungal communities were dominated by available potassium contents. SEM (structural equation model) showed that land use has direct and indirect effects on bacterial composition, while only indirect effects on fungal by land use. Land use indirectly affected bacterial composition through effects on soil moisture, clay and available potassium contents, whereas through effects on clay and available potassium for fungal composition. Land use exhibited greater impacts on bacterial composition than fungal composition, implying bacteria was more sensitive to land use changes compared to fungi in the dry-hot valley. Considering the low level of total potassium in soil under SL and CT, elevated potassium fertilizer would be a beneficial pathway to improve soil microbial composition and soil nutrients in the dry hot valley.

Key word: Land use, Soil microbial community, Dry-hot valley, Soil properties, Structural equation model.

How to cite: Liu, T., Rong, L., Duan, X., and Chen, Z.: Land use types influence soil microbial community through effects on soil properties in the dry-hot valley region in southwestern China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3963, https://doi.org/10.5194/egusphere-egu21-3963, 2021.

The slope runoff caused by rainstorm is the main cause of serious soil and water loss in the loess hilly area, the grassland vegetation has a good inhibitory effect on the slope runoff, it is of great significance to reveal the role of grassland vegetation in the process of runoff generation and control mechanism for controlling soil erosion in this area. In this study, typical grassland slopes in hilly and gully regions of the loess plateau were taken as research objects. Through artificial rainfall in the field, the response rules of slope rainfall-runoff process to different grass coverage were explored. The results show that: (1) The time for the slope flow to stabilize is prolonged with the increase of vegetation coverage, and shortened with the increase of rainfall intensity; (2) At 60 mm·h ⁻¹ rainfall intensity, the threshold of grassland vegetation coverage is 75.38%; at 90 mm·h ⁻¹ rainfall intensity, the threshold of grassland vegetation coverage is 90.54%; at 120 mm·h ⁻¹ rainfall intensity, the impact of grassland vegetation coverage on runoff is not significant; (3) the Reynolds number and Froude number of slope flow are 40.07‒695.22 and 0.33‒1.56 respectively, the drag coefficient is 1.42‒43.53. Under conditions of heavy rainfall, the ability of grassland to regulate slope runoff is limited. If only turf protection is considered, about 90% of grassland coverage can effectively cope with soil erosion caused by climatic conditions in loess hilly and gully regions. Therefore, in loess hilly areas where heavy rains frequently occur, grassland's protective effect on soil erosion is obviously insufficient, and investment in vegetation measures for trees and shrubs should be strengthened.

How to cite: Zhang, Q., Lv, X., Chen, R., Ni, Y., and Ma, L.: Regulation and Critical Threshold of Grass Cover on Slope Runoff in LoessHilly Gully Region under Artificial, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4363, https://doi.org/10.5194/egusphere-egu21-4363, 2021.

In the past 60 years, climate changes and underlying surface of the watershed have affected the structure and characteristics of water resources to a different degree It is of great significance to investigate main drivers of streamflow change for development, utilization and planning management of water resources in river basins. In this study, the Huangshui Basin, a typical tributary of the upper Yellow River, is used as the research area. Based on the Budyko hypothesis, streamflow and meteorological data from 1958-2017 are used to quantitatively assess the relative contributions of changes in climate and watershed characteristic to streamflow change in research area. The results show that: the streamflow of Huangshui Basin shows an insignificant decreasing trend; the sensitivity coefficients of streamflow to precipitation, potential evapotranspiration and watershed characteristic parameter are 0.5502, -0.1055, and 183.2007, respectively. That is, an increase in precipitation by 1 unit will induce an increase of 0.5502 units in streamflow, and an increase in potential evapotranspiration by 1 unit will induce a decrease of 0.1055 units in streamflow, and an increase in the watershed characteristic parameter by 1 unit will induce a decrease of 183.2007 units in streamflow. Compared with the reference period (1958-1993), the streamflow decreased by 20.48mm (13.59%) during the change period (1994-2017), which can be attribution to watershed characteristic changes (accounting for 73.64%) and climate change (accounting for 24.48%). Watershed characteristic changes exert a dominant influence upon the reduction of streamflow in the Huangshui Basin.

How to cite: Lv, X., Li, S., Ni, Y., Zhang, Q., and Ma, L.: Quantitative estimation on contribution of climate changes and watershed characteristic changes to decreasing streamflow in the Huangshui Basin, China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4131, https://doi.org/10.5194/egusphere-egu21-4131, 2021.

Abstract: As a huge metropolis, the highly intensive development and utilization of underground space in Shanghai has become the distinct trend of urban construction. Combined research among more than 100 industrial and civil construction projects in the city finds that soil erosion during the construction of underground works accounts for a significant proportion (50%~60%) of the totality of soil erosion or degradation. In order to further promote the precise management and control of water and soil conservation in the procedure of construction engineering projects, this paper analyzes the relationship between foundation pit supporting measures and water and soil conservation results in typical underground engineering examples. Through summing up the high frequency risk points of water and soil loss caused by underground engineering of housing construction projects in Shanghai, several positive methods for preventing and controlling water and soil erosion could be contributed correspondingly for the future work, such as pretreatment of the drilling caving of bored piles, and making full use of the soil produced by underground excavation.

Key words: underground engineering; risk analysis; water and soil conservation measures

How to cite: Tang, H.: Soil erosion and its prevention measures during the construction period of underground engineering: a case study in the city Shanghai, China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16497, https://doi.org/10.5194/egusphere-egu21-16497, 2021.

Severe soil erosion occurs in southwestern China owing to the large expanses of human disturbance and sloping land. This field monitoring study was conducted during the rainy season to record the rainfall events, runoff, sediment yield, nitrogen, and phosphorous loss in 20-, 40-, and 60-m plots under conditions of artificial disturbance or natural restoration on a 15° slope in the purple soil area of southwestern China. The concentrations and loss amounts of total nitrogen (TN), total dissolved nitrogen (TDN), ammonium-nitrogen (NH4-N) and nitrate-nitrogen (NO₃-N), total phosphorus (TP), total dissolved phosphorus (TDP) and orthophosphate (PO₄-P) were comparatively determined. The highest N concentration was observed in long duration and soft rainfall events across all plots. The highest P concentration in artificial disturbed plots was found in long duration and intensive rainfall events while it was recordeds for measured variables were dominantly recorded under the long duration and lowest soft rainfall events in naturally restored plots intensity., while The the highest loss amounts for N and P in different forms for these variablesalmostmostly appeared under high rainfall intensity. Land disturbances differed orthophosphate PO₄-P concentration in 20--m plot and and loss amounts of of measured variables N and P with different forms across in all plots. Plot lengths differed total dissolved phosphorus TDP concentration in natural restored plot and loss amounts of total dissolved nitrogenTDN and orthophosphate PO₄-P in artificially disturbed plots. Naturally restoration reduced loss amounts of total nitrogen and total phosphorus by 69.4%62.14-79.05% and 79.28-83.43% TN, 68.8% TDN, 71.2% NH₄-N, 74.3% NO₃-N, 81.5% TP, 71.9% TDP and 70.0% PO₄-P loss amounts comparedrelative to artificial disturbance, respectively. There were significant interrelationships among N and P concentrations in different forms in two land disturbance plots, while nitrate-NO₃-nitrogenN concentration hadwas significantly negatively negative correlatedion with rainfall intensity and runoff rate in artificialally disturbanceed plots. Rainfall intensity was logarithmically correlated with TN, NO₃-N concentrations in artificially disturbed plots and with NO₃-N concentration in naturally restored plots. Runoff rate was logarithmically correlated with TN, TDN and NO₃-N concentrations in artificially disturbed plots. Our results highlight the effects of land disturbance and plot length on nutrient losses in sloping land.

How to cite: Liang, K. and He, B.: Naturally rainfall-induced changes in runoff-associated nitrogen and phosphorus losses in purple soil area: roles of land disturbance and plot length, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13919, https://doi.org/10.5194/egusphere-egu21-13919, 2021.

Changes in land use can result in soil erosion and the loss of soil organic carbon (SOC). However, the individual contribution of different land use types on SOC variability as well as the combined impacts of land use and soil erosion are still unclear. The aims of the present study were to: (1) evaluate soil erosion and SOC contents under different land use types, (2) identify the influences of soil depth and land use on SOC content, and (3) determine the contribution of land use and soil erosion on SOC variability. We assessed the SOC and total soil nitrogen (TSN) contents under three types of land use in the dry-hot valley in southern China. Caesium-137 (¹³⁷Cs) and excess lead-210 (²¹⁰Pb_ex) contents were also measured to determine soil-erosion rates. Land use was found to significantly affect soil erosion, and erosion rates were higher in orchard land (OL) relative to farmland (FL), which is in contrast with previous study results. SOC and TSN contents varied significantly between the three land use types, with highest values in forest land (FRL) and lowest values in OL. SOC was found to decrease with decreasing soil depth; the highest rate of reduction occurred in the reference site (RS), followed by FRL and FL. The interaction between soil erosion and land use significantly impacted SOC in the soil surface layer (0–12 cm); the direct impact of soil erosion accounted for 1.5% of the SOC variability, and the direct or indirect effects of land use accounted for the remainder of the variability. SOC content in deep soil was mainly affected by factors related to land uses (89.0%). This quantitative study furthers our understanding on the interactive mechanisms of land use and soil erosion on changes in soil organic carbon.

How to cite: Li, Y., Duan, X., Li, Y., Li, Y., and Zhang, L.: Interactive effects of land use and soil erosion on soil organic carbon in the dry-hot valley region of southern China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2556, https://doi.org/10.5194/egusphere-egu21-2556, 2021.

Dahuofang reservoir (DHFR) is one of the most important drinking water sources in Liaoning province, China. The processes of total phosphorus (TP) concentration, flux and retention rate are very important to the water quality management and drinking water safety for the reservoir. Based on the monitoring data of meteorology, hydrology, water quality and sediment, etc. at the controlled stations of Dahuofang catchment during 1992-2017, The suspended sediment centration(SSC) and TP concentration variation and differences from upper to lower reach of DHFR  during floods in 2010 and 2013 are analyzed and compared respectively. Based  on the  mass balance equation of TP and the related fluxes formula at the different boundaries, the stocking processes in both the overlying water and the active surface sediment layer are solved. The results revealed the TP accumulation variation in the overlying water and the surface sediment layer, together with the controlling mechanism of TP concentration in overlying water under different floods events. Moreover, the results discovered that the combination of flood and dry hydrological rhythms is very important to maintain the dynamic balance of accumulated sediment and TP in the reservoir. The study does not only provide the effective calculation method forthe TP flux, accumulation and retention rate in the large reservoir, but also partly supply a new eyesight on the sediment nutrient control and related continuable management  for large reservoirs in north China.

How to cite: Huang, G., Li, X., Sun, M., and Lei, K.: Study on the concentration, flux, occurrence and retention processes of total phosphorus in Dahuofang reservoir, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6173, https://doi.org/10.5194/egusphere-egu21-6173, 2021.

Agricultural non-point sources (ANPS) pollution are considered to pose risks to water quality in Three Gorges Reservoir Areas (TGRA), especially when those pollution source comes from the hydrologically sensitive areas (HSAs) that generate surface runoff pathways. Therefore, it is necessary to identify the critical source areas (CSAs) or the sensitive regions of pollutants from agricultural lands in order to control and mitigate ANPS pollution effectively. In this study, an improved method integrating the Phosphorus Index (PI) and the Soil Topographic Index (STI) was applied to predict the risk of phosphorus loss and delineate the CSAs of phosphorus in a typical agricultural watershed in TGRA, China. The results showed that using a STI threshold value of 8.5, the HSA was identified 22.08% of watershed areas. The intersection of above two parts account 5.47% of the total watershed, compared with 24.41% of watershed areas based on an existing approach that uses just one criterion. As the results showed , the CSAs of phosphorus loss were mainly located near streams, with high or relatively high soil phosphorus contents or phosphorus fertilizer, or intense soil erosion are observed. The calculated results are in good agreement with the actual situation. Since the approach is based on GIS, and is a relatively simple application uses readily available geospatial data, therefore the technic could be used to improve cost-effectiveness and provide a useful screening tool for water resource managers responsible for identifying and remediating critical NPS source areas. 

How to cite: Zhou, Y. and Li, Z.: Phosphorus critical source areas identification in an agricultural watershed of Three Gorges Reservoir Area, China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15988, https://doi.org/10.5194/egusphere-egu21-15988, 2021.

Although the concept of ecological drought was first defined by the Science for Nature and People Partnership (SNAPP) in 2016, there remains no widely accepted drought index for monitoring ecological drought. Therefore, this study constructed a new ecological drought monitoring index, the standardized ecological water deficit index (SEWDI). The SEWDI is based on the difference between ecological water requirements and consumption, referred to as the standardized precipitation index (SPI) method, which was used to monitor ecological drought in Northwestern China (NWRC). The performances of the SEWDI and four widely-used drought indices [standardized root soil moisture index (SSI), self-calibrated Palmer drought index (scPDSI), standardized precipitation-evaporation drought index (SPEI), and SPI) in monitoring ecological drought were evaluated through comparing the Pearson correlations between these indices and the standardized normalized difference vegetation index (SNDVI) under different time scales, wetness, and water use efficiencies (WUEs) of vegetation. Finally, the rotational empirical orthogonal function (REOF) was used to decompose the SEWDI at a 12-month scale in the NWRC during 1982–2015 to obtain five ecological drought regions. The characteristics of ecological drought in the NWRC, including intensity, duration, and frequency, were extracted using run theory. The results showed that the performance of the SEWDI in monitoring ecological drought was highest among the commonly-used drought indices evaluated under different time scales [average correlation coefficient values (r) between SNDVI and drought indices: SEWDI= 0.34, SSI= 0.24, scPDSI= 0.23, SPI= 0.20, SPEI= 0.18), and the 12-month-scale SEWDI was largely unaffected by wetness and WUE. In addition, the results of the monitoring indicated that serious ecological droughts in the NWRC mainly occurred in 1982–1986, 1990–1996, and 2005–2010, primarily in regions I, II, and V, regions II, and IV, and in region III, IV, and V, respectively. This study provides a robust approach for quantifying ecological drought severity across natural vegetation areas and scientific evidence for governmental decision makers.

How to cite: Jiang, T. and Su, X.: A novel index for ecological drought monitoring based on ecological water deficit: a case study of Northwestern China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5439, https://doi.org/10.5194/egusphere-egu21-5439, 2021.

Determining the impacts of environmental and socioeconomic factors on nitrogen (N) and phosphorus (P) loss in the watershed is critical to reducing non-point source (NPS) pollution. This paper, we set 13 sampling points in the main stream and tributaries of watershed and sampled every two weeks from 2018 to 2020 to monitor the total nitrogen (TN) and total phosphorus (TP) concentration in the waterbodies. Twenty-six potential influencing factors affecting the nitrogen and phosphorus loss in the watershed were selected. The partial least squares regression (PLSR) was used to determine the relationship between TN and TP concentrations in the watershed and the 26 selected potential influencing factors. The results showed that the mean TN concentrations and mean TP concentrations in the dry season (11.42 mg·L⁻¹ and 0.09 mg·L⁻¹, respectively) were both less than those in the wet season (13.20 mg·L−1 and 0.11mg·L−1, respectively). The optimal PLSR model explained 69.6%, 73.1% and 66.1% of the TN concentration variability, and 65.7%, 79.5% and 67.4% of the TP concentration variability during annual, dry season and wet season, respectively. According to the importance of the variables in the predicted value (VIP), topographic wetness index (TWI), planting structure (PS), interspersion and juxtaposition index (IJI), Orchard land use (OP), nitrogen fertilizer application (NF), per capita income (INCOME) and catchment area (AREA) were the key factors affecting TN concentration, whereas topographic wetness index (TWI), interspersion and juxtaposition index (IJI), population density (POP), slope gradient (SLOPE) and hypsometric integral (HI) were the key controlling factors of TP concentration. In addition, TN concentration was affected by cropland land use (CP) during the dry season and proportion of labor (LABOR) and per capita agricultural land area (ALA) during the wet season. TP concentration was affected by mean patch size (AREA_MN), phosphate fertilizer application (PF) and patch density (PD) during the dry season and residential area (RP) and values during the wet season. This study illustrates the impact of environmental and socioeconomic factors on NPS pollution, and can be used as a guide for effective NPS pollution control and water quality management.

How to cite: Deng, J. and Li, Z.: The impacts of environmental and socioeconomic factors on the non-point source pollution in a small watershed in the Three Gorges Reservoir Area, China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16225, https://doi.org/10.5194/egusphere-egu21-16225, 2021.

Abstract: In view of the weak research on the rheological characteristics involved in the variation of the fluid movement caused by the storm runoff carrying a large amount of pollutants and sediments, this study uses the NDJ-5S rotary viscometer and the self-made slim tube viscometer of Northwest Agriculture and Forestry University. On the basis of the research, the influence of pollutants on the rheological characteristics of high-concentration sandy water flow is studied. The results show that the NDJ-5S rotary viscometer can be used well under the sand content of less than 300kg/m³. The double vertical tube slim tube viscometer made by Northwest A&F University can better simulate the sand content of 0～800kg/m³; The structure of flocculation between particles in sandy water flow will affect the viscosity of muddy water, and the concentration of sediment and other pollutants will have a certain impact on flocculation. Under the same conditions, the concentration of pollutants increases (0～440kg/m3), the viscosity coefficient of fluid increases (90%～114%), and the variation of sand content from Newtonian body to Bingham body is about 300～400kg/m³, The influence of pollutants on the variation points of rheological properties is not significant.

Keywords: pollutants; sediment; variation; viscometer; Newtonian fluid; Bingham fluid

Funding: This study was funded by the National Natural Science Foundation of China (No. 41877078, 41371276), Key research and development project of Shaanxi Province (2020ZDLSF06-03-01), National Key Research and Development Program of China (No. 2017YFC0504703) and Knowledge Innovation Program of the Chinese Academy of Sciences (No. A315021615). 

How to cite: Zhang, Y., Gao, J., Gao, Z., Kang, Y., Wang, Z., Wang, L., Zhou, F., Liu, S., Li, X., and Ji, M.: Influence of pollutants on rheological characteristics of sediment flow, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3828, https://doi.org/10.5194/egusphere-egu21-3828, 2021.

Abstract: Outcrops of rock strata in the Karst Trough Valley Area often form angles with slopes, thus making micro landforms complicated and altering significantly paths of concentrated flows, and consequently bringing about great changes in characteristics of the flows. So, it’s important to study hydraulic characteristics of the concentrated flows relative to angle between rock strata and slope. To that end, a flume experiment, designed to have combinations of three slope gradients (10°,15° and 20°), three flow rates (5, 7.5 and 10 L·min-1) and six angles between the rock strata and slope (30°, 60°, 90°, 120°, 150° and 180° (0°)), was carried out. Results show that hydraulic characteristics of a concentrated flow varied significantly with the angle between the rock stratum and slope. Reynolds number (Re) of the concentrated flow changed with duration of the scouring in a complicated trend, but exhibited a significant trend of increasing with rising flow rate, and an insignificant one of changing with slope gradient. And it varied in the range of 517~3343 in the experiment. Darcy-Weisbach friction coefficient (f) of the concentrated flow increased with rising slope gradient and with scouring going on, but decreased with rising flow rate. And it varied in the range of 0.62~5.70 in the experiment. The relationship of Re with angles between rock strata and the slope was not significant, but that of f varied with combinations of slope gradient and flow rate. The coupling relationship between f and Re was influenced significantly by the angle between the rock stratum and the slope. It could be better described with a logarithmic equation when the angle between the rock stratum and the slope was narrower than 90°, and with a power function equation when the angle between the rock stratum and the slope was wider than or equal to 90°. In the experiment, when Re<1791, the relationship between f and Re was not apparent, but when Re>1791, it was significantly positive. To sum up, f and Re and their relationship vary with the angle between the rock stratum and the slope. The findings in this experiment may provide strong data support for establishing soil erosion prediction models in the Karst Trough Valley Area.

How to cite: Zeng, C., Zeng, R., and He, B.: Hydraulic Characteristics of Concentrated Flow Relative to Angle between Rock Strata and Slope in the Karst Trough Valley Area, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13866, https://doi.org/10.5194/egusphere-egu21-13866, 2021.